Experimental evolution of sperm competitiveness in a mammal

Background  

When females mate with multiple partners, sperm from rival males compete to fertilise the ova. Studies of experimental evolution have proven the selective action of sperm competition on male reproductive traits. However, while reproductive traits may evolve in response to sperm competition, this does not necessarily provide evidence that sperm competitive ability responds to selection. Indeed, a study of Drosophila failed to observe divergence in sperm competitive ability of males in lines selected for enhanced sperm offence and defence.     

Experimental alteration of litter sex ratios in a mammal

Adaptive theory predicts that mothers would be advantaged by adjusting the sex ratio of their offspring in relation to their offspring's future reproductive success. Studies investigating sex ratio variation in mammals, including humans, have obtained notoriously inconsistent results, except when maternal condition is measured around conception. Several mechanisms for sex ratio adjustment have been proposed. Here, we test the hypothesis that glucose concentrations around conception influence sex ratios. The change in glucose levels resulted in a change in sex ratios, with more daughters being born to females with experimentally lowered glucose, and with the change in glucose levels being more predictive than the glucose levels per se. We provide evidence for a mechanism, which, in tandem with other mechanisms, could explain observed sex ratio variation in mammals.     

Experimental evidence for predation risk sensitive oviposition by a mosquito, Culiseta longiareolata

1. Females should choose to oviposit in habitats where risk of predation and competition are low. The ovipositional responses of a mosquito, Culiseta longiareolata, to a predator and to species sharing the same trophic level as this mosquito (controphic species) were assessed experimentally in outdoor artificial pools. 2. The predator, larval Anax imperator, which strongly reduced larval C. longiareolata survival, resulted in a 52% reduction of C. longiareolata egg rafts. The controphic species (primarily Daphnia magna), which had a small but statistically significant negative effect on the survival of C. longiareolata larvae, did not have a statistically significant influence on the number of egg rafts. 3. Laboratory trials indicated that only a small fraction of the reduced number of egg rafts seen in predator pools may be due to consumption of the egg rafts by A. imperator. 4. The experimental evidence indicates that the reduced number of C. longiareolata egg rafts found in the presence of A. imperator is due largely to oviposition habitat selection, i.e. C. longiareolata females choose pools with low risk of predation for their offspring.     

Temporal and spatial variation in age-specific survival rates of a long-lived mammal, the Hawaiian monk seal

Estimates of variability in pinniped survival rates are generally based on observations at single sites, so it is not certain whether observed rates represent the whole population. Here, we provide a comprehensive analysis of spatio-temporal variation in age-specific survival rates for endangered Hawaiian monk seals (Monachus schauinslandi) based on capture-recapture analyses of more than 85% of the pups weaned in this population over the last two decades. Uniquely, these data have been collected from six subpopulations, encompassing all major breeding sites across its 1800 km long core range. Analyses of individual subpopulations revealed similar patterns in age-specific survival, characterized by the relatively low survival rates from weaning to 2 years of age, intermediate rates to 4 years of age, and then by relatively high 'mature' survival rates until 17 years of age, after which a senescent decline was observed. Juvenile, subadult and adult survival rates all varied significantly over time. Trends in survival among subpopulations were coherent with their relative geographical positions, suggesting regional structuring and connectedness within the archipelago. Survival rates for different age classes tended to be positively correlated, suggesting that similar factors may influence the survival for seals of all ages.     

Habitat-specific demography: evidence for source-sink population structure in a mammal,the pika

Theory suggests that populations may persist in sink habitats that cannot support replacement-level birth rates. Although it is commonly believed that organisms that can actively select habitat should rarely occur in sinks, the frequency of use of sinks in free-ranging species is not well-documented. We found that a population of American pikas ( Ochotona princeps, Lagomorpha) inhabiting distinct alpine habitats (meadow and snowbed) in Wyoming, USA, had habitat-specific demographic rates that produced a source-sink population structure. Population size increased in both habitats in summer and declined in both habitats in winter, with populations in snowbeds increasing more during summer and decreasing more over winter. Birth rates were consistently higher in meadows and populations in meadows had a consistently higher finite rate of increase (lambda, from life tables) than did those in snowbeds, for which lambda was far below that needed for replacement. Patterns of immigration, population structure, and temporal variation in population size were as expected if meadows were functional sources and snowbeds functional sinks. Patterns of snowmelt differed between habitats, predicted the critical difference in birth rates between habitats, and are a likely primary cause of the differences in habitat-specific birth rates that we observed. This study provides a clear example of source-sink population structure for a mammal.     

Experimental evidence for multistability in a photobiochemical system

The kinetic behavior of a typical Hill reaction catalyzed by thylakoids and using the oxidized form of 2,6-dichloroindophenol (DCPIPox) as the artificial electron acceptor, is considered. Here, the light absorption process and the reduction of DCPIPox are autocatalytically coupled, leading to the occurrence of multiple steady states with respect to either the acceptor concentration or the incident light intensity. Experimental evidence is presented for both cases and the emergence of autocatalysis is discussed. The effect of the spatial arrangement on the global behavior of the system described is emphasized.     

Comparative evidence for a cost to males of manipulating females in bushcrickets

Recent theoretical and empirical research on sexual conflicthas tended to focus on the costs to females of being manipulatedby males. The costs to males associated with the productionof manipulative traits have received relatively little attention.In numerous insects, including bushcrickets (Orthoptera: Tettigoniidae),males are known to transfer substances in the ejaculate thatinhibit the receptivity of females to further matings in a dose-dependentmanner. The aim of this study was to test the prediction that,across bushcricket taxa, larger ejaculates and nuptial giftswill be associated with, on the one hand, longer sexual refractoryperiods in females and, on the other hand, longer sexual refractoryperiods in males. Data on the duration of the sexual refractoryperiod in both males and females, together with ejaculate mass,spermatophylax mass, and male body mass, were obtained for 23species of bushcricket. Both comparative analysis by independentcontrasts and species regression revealed a positive relationship,across taxa, between the duration of the female's sexual refractoryperiod and both relative ejaculate mass and relative nuptialgift mass. Positive relationships were also found between theduration of the male's sexual refractory period and both relativeejaculate mass and relative nuptial gift mass, indicating thatthere is a trade-off between resources spent on spermatophoresize and the male's potential mating rate. This appears to bethe first comparative evidence that there is a cost to malesassociated with manipulating the remating behavior of theirmates.     

Experimental evidence for a semi-flexible conformation for arabinoxylans

Purified water-soluble arabinoxylans from wheat flour were deferuloylated and fractionated into six fractions by graded ethanol precipitation. Further fractionation by HPSEC on Sephacryl S500 resulted in 48 subfractions with low polydispersity index. Conformational characteristics (persistence length q, hydrodynamic parameter v and Mark-Houwink exponent a) were similar among all subfractions and fitted with a semi-flexible conformation, whatever their structural characteristics. Substitution degree of the xylan backbone by arabinose residues has no influence on the conformation of arabinoxylans.     

Female-biased dispersal under conditions of low male mating competition in a polygynous mammal

Sex-biased dispersal is a common phenomenon in birds and mammals. Competition for mates has been argued to be an important selective pressure favouring dispersal. Sexual differences in the level of intrasexual competition may produce asymmetries in the costs-benefits balance of dispersal and philopatry for males and females, which may favour male-biased dispersal in polygynous species such as most mammals. This being the case, condition-dependent dispersal predicts that male-bias should decrease if mating competition relaxes. We test this expectation for red deer, where male-biased dispersal is the norm. In southwestern Spain, red deer populations located in nonfenced hunting estates presented altered structures with sex ratio strongly biased to females and high proportion of young males. As a consequence, mate competition in these populations was lower than in other, most typical red deer populations. We found that, under such conditions of altered population structure, dispersal was female-biased rather than male-biased. Additionally, mate competition positively related to male dispersal but negatively to female dispersal. Other factors such as resource competition, age of individuals and sex ratio were not related to male or female dispersal. Males may not disperse if intrasexual competition is low and then females may disperse as a response to male philopatry. We propose hypotheses related to female mate choice to explain female dispersal under male philopatry. The shift of the sex-biased dispersal pattern along the gradient of mate competition highlights its condition-dependence as well as the interaction between male and female dispersal in the evolution of sex-biased dispersal.     

Mass spectrometric evidence for long-lived protein adducts of 4-oxo-2-nonenal

Substantial work has been carried out to elucidate the nature of protein modification by 4-hydroxy-2-nonenal (HNE) and its relatives. Its keto cousin, 4-oxo-2-nonenal (ONE), which arises from linoleic acid oxidation independently of HNE, was previously reported to form Michael adducts with His and Cys that can subsequently, in part, condense with Lys residues to give imidazolylpyrrole cross-links. Despite mass spectrometric evidence also for ONE-Lys Michael adducts, the latter do not accumulate in solution. A long-lived adduct that has the same mass as the ONE Lys Michael adduct is suggested instead to be the isomeric 4-ketoamide that arises, along with other adducts, from the reversibly-formed ONE Lys Schiff base. The Lys-ketoamide and His-Lys imidazolylpyrrole cross-links appear to be unusually prominent markers of stable protein modification by ONE.     

Experimental evidence for a persistent spore bank in Sphagnum

Spore capsules of four Sphagnum species were buried at different depths in peat on a bog. Spore viability was determined after 0, 1, 2 and 3 yr. Viability generally declined with time, but viable spores were still found at all depths after 3 yr. The light-coloured spores of S. balticum and S. tenellum retained their viability better than the darker spores of S. fuscum and S. lindbergii . Survival was highest under wet but aerobic conditions, but was also high under humid or periodically desiccated conditions. By contrast, most spores stored under wet, anaerobic conditions died within 2–3 yr. These results, and predictions from them, are not consistent with earlier results for spores of long-lived and dominant bryophytes, or for seeds of phanerogams of undisturbed wetlands and forests. There was no correlation between spore size and longevity across species, but the small spores from small capsules of S. balticum and S. tenellum generally showed higher viability than those from the medium-sized and large capsules of the same species. This suggests a positive intraspecific relationship between longevity and dispersal distance. There was an indication of conditional dormancy, controlled by weather, in Sphagnum spores. The experiments indicate that Sphagnum spores can form a long-term persistent spore bank under suitable conditions, with a half-life of between 1 and 20 yr (mean across species of 2.6 and 5.0 yr at two depths studied), and with potential values in individual spore capsules of several decades, or even of centuries. Sphagnum spores kept refrigerated showed 15–35% viable spores after 13 yr. The capacity to form a persistent spore bank that can be activated whenever favourable conditions occur might help explain the wide geographical distribution of many Sphagnum species in the boreal and temperate zones, where they have managed to colonize almost every suitable patch of acidic, nutrient-poor wetland.     

Experimental evidence for the adaptive response of aquatic invertebrates to chronic predation risk

As acute stress induced by predation risk can generate significant oxidative damage, prey organisms are forced to balance their defence reaction and the cost of activating the cellular defence system. Stress tolerance differs significantly among species; therefore predator pressure indirectly shapes the community structure. To test adaptation abilities of amphipod crustaceans (Dikerogammarus villosus and Gammarus jazdzewskii) we exposed them to acute (35 min.) and chronic (1 or 7 days) predation risk (the Eurasian perch). We measured respiration (related to metabolic rate), cellular defence systems (antioxidant enzyme (catalase) activity and heat shock protein (Hsp70) concentration), and the level of oxidative damage (thiobarbituric acid reactive substances (TBARS) concentration). Both amphipods increased their respiration rate in the presence of predation cues, irrespective of the duration of their pre-exposure to danger. This increase in D. villosus was initiated more quickly (immediately vs. after 10 min. of the test) and lasted for a longer time (20 vs. 10 min.) than in G. jazdzewskii. However, only G. jazdzewskii after a short exposure to predation risk exhibited an increase in its catalase activity, Hsp70 concentration and oxidative damage. No changes in these parameters were exhibited by D. villosus or after a chronic exposure of G. jazdzewskii to predation cues. Our results show that prey organisms are able to reconfigure their physiology to maintain increased metabolic rate under prolonged predator pressure and, at the same time, reduce oxidative damage as well as costs related to anti-oxidant defence.     

Experimental evidence that sentinel behaviour is affected by risk

Sentinels are a conspicuous feature of some cooperative societies and are often assumed to provide benefits in terms of increased predator detection. Similar to other cooperative behaviours, variation in investment in sentinel behaviour should reflect variation in the benefits of such behaviour. However, evidence for this is inconclusive: to date experiments have manipulated the cost of sentinel behaviour, and considerations of changes in the benefits of sentinel activity on investment patterns are lacking. Here, we experimentally manipulated the benefits of sentinel behaviour in the cooperatively breeding pied babbler (Turdoides bicolor) to assess whether this had any impact on sentinel activity. We simulated the presence of an unseen predator using playbacks of heterospecific alarm calls, and the presence of an actual predator using a model snake. In both cases, the increase in perceived predation risk caused an increase in sentinel activity, demonstrating that investment in sentinel activity increases when the benefits are greater.     

Experimental binding of lead to a low cost on biosorbent: Nopal (Opuntia streptacantha)

The use of nopal cladodes (Opuntia streptacantha) as raw material for Pb(2+) biosorption was investigated. Batch experiments were carried out to determine Pb(2+) sorption capacity and the efficiency of the sorption process under different pH, initial Pb(2+) and nopal biomass concentrations. The experimental data showed a good fit to Langmuir and Freundlich isotherms models. The maximum adsorption capacity for Pb(2+) was 0.14 mmol g(-1) with an efficiency higher than 94% (pH 5.0 and 2.5 g L(-1) nopal biomass). The Pb(2+) kinetics were best described by the pseudo-second-order rate model. The rate constant, the initial sorption rate and the equilibrium sorption capacity were determined. The practical implication of this study is the development of an effective and economic technology in which the nopal biomass did not undergo any chemical or physical pretreatment, which added to nopal abundance in Mexico and its low cost makes it a good option for Pb(2+) removal from contaminated waters.     

Predation risk as a cost of reproduction

Predation risk as a cost of reproduction in animals has recently received increased empirical and theoretical attention. Higher risk may be associated with all stages of reproduction. Examples of evolutionary responses to this increased risk include habitat choice, duration and timing of display and copulation, changes in brightness of breeding coloration, and changes in life history traits such as age of reproduction and reproductive effort.     

Development of a simple and low cost microbioreactor for high-throughput bioprocessing

A simple microbioreactor for high-throughput bioprocessing made from low cost polymer polytetrafluoroethylene (PTFE) tubes with a working volume of 1.5 ml is described. We have developed a microfluidic system that handles a small population of cells of a model microorganism, Pseudomonas aeruginosa DS10-129. Under the conditions of the microbioreactor, the organism produced extracellular secondary metabolites by using nutrient broth modified with glycerol. Pyocyanins were isolated from the fermented medium as a metabolite of interest. Antibiotic properties of pyocyanin were effective against a number of microorganisms such as Staphylococcus aureus, S. epidermis, Bacillus subtilis, Micrococcus luteus and Saccharomyces cerevisiae. Batch fermentation of the model organism in the microbioreactor was compared to shake-flask and conventional bench fermenter methods. Results obtained from the microbioreactor compared favourably with the conventional processes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Development of a risk assessment for BSE in the aquatic environment

Bovine spongiform encephalopathy (BSE) is believed to be transmitted by the ingestion of proteinaceous agents called prions which accumulate in the brain and spinal cord of infected bovines. Concern has been expressed about the risks of transmission of BSE to humans through BSE prions discharged to the aquatic environment from rendering plants, abattoirs and landfills. The disease-related form of the prion protein is relatively resistant to degradation, and infectivity decays rather slowly in the environment. Levels of disinfection used for drinking water treatment would have little effect. This paper presents the assumptions which were used to model the risks from a rendering plant disposing of cull cattle carcasses in the catchment of a chalk aquifer which is used for a drinking water abstraction. The risk assessment approach focused on identifying the hydrogeological and physical barriers which would contribute to preventing BSE infectivity gaining entry to the aquifer. These barriers included inactivation of BSE agent by the rendering process, removal from the effluent by treatment at the plant, filtration and adsorption in the clay and chalk, and dilution in the ground water. The importance in environmental risk assessment of the cow-to-man species barrier is considered. Two key conclusions about the environmental behaviour of the BSE agent are that prion proteins are 'sticky' and bind to particulates, and that the millions of BSE prion molecules comprising a human oral ID₅₀ are subject to some degree of dispersion and hence dilution in the environment. Assuming the rendering plant processes 2000 cull cattle carcasses per week, the risks to drinking water consumers were estimated to be remote. Indeed, even using worst case assumptions an individual would have to consume 2 l d⁻¹ of tap water for 45 million years to have a 50% chance of infection through drinking water drawn from the aquifer.     

Multiple captures provide evidence of small mammal social behavior

Social behavior of small mammals living under natural conditions often is inferred from live-trapping data, particularly from incidents in which two or more individuals are captured together in a trap. We examined whether multiple-capture data from a long-term study of prairie voles (Microtus ochrogaster) and meadow voles (Microtus pennsylvanicus) were consistent with well-known species differences in social behavior (whereas prairie voles are highly social and display monogamy, meadow voles are less social and promiscuous). When possible, we also examined multiple captures of two nontarget species, northern short-tailed shrews (Blarina brevicauda) and western harvest mice (Reithrodontomys megalotis). Percent of total captures that were multiple captures and percent of total adult captures that were male–female captures were highest for prairie voles and lowest for meadow voles; values for harvest mice and shrews were in between those of the vole species, but more similar to values for meadow voles. Repeat captures of the same male–female pair occurred most commonly in prairie voles, and multiple captures of this species typically involved individuals from the same social group. Multiple captures of adults and juveniles were more common in prairie voles than meadow voles, except for captures of at least one adult male and at least one juvenile, which did not differ between the two vole species. Multiple capture data for prairie voles and meadow voles were largely consistent with established species differences in social behavior, suggesting that such data can provide an accurate indication of social and mating systems of small mammals.